Magnetic material



loys of iron and nickel.

Patented Apr. 14, 1931 ROBERT GOLDSCHMIDT, OF 'BERLIN-KARLSHORST, AND HELMUT SPRUNG, OF BERLIN- FRIEDRICHSHAGEN, GERMANY, ASSIGN CORPORATION OF NEW YORK OBS TO GENERAL ELECTRIC COMPANY, A

MAGNETIC, MATERIAL No Drawing. Application filed July 21, 1930, Serial No. 469,632, and in Germany August 28, 1929.

Thisinvention relates to electromagnetic materials for use in weak electromagnetic fields such as are present in the cores of loading coils, and magnetic wire or tape spirally applied to conductors to increase the inductance thereof, and methods of producing such materials.

An object of the invention is to increase the constancy of permeability of niagnetic materials. 1

With the development of long-distance signalling-technique, magnetic materials came into demand for windings, transmitters, Krarup helically applied loading, etc. which possess excellent magnetic properties, particularly in weak fields. More particularly has importance been placed upon the attaimnent of high initial permeability. The known processes for the production of magnetic wires, bands, plates or the like, without exception are designed to attain a high initial permeability of the final products: This end can be attained also with al- With a 78/22% nickel-iron alloy, an initial permeability of 10,000 can, for instance, be obtained. It is disadvantageous, that with these alloys, the hysteresis and the current-dependency of the magnetic values, so closely connected with it, in connection with weak fields, also increase to an extraordinary degree: (Compare Jordan, Magnetis che Konstanten E. N. T., vol. 1, No. 1). Nickel-iron alloys usually show a poor degree of magnetic stability, i. e. their properties change considerably, with weak fields, during or after they I are subjected to intense fields. A further disadvantage of the wires or similar materials made from highly permeable alloys, is their sensitiveness with regard to mechanical strain and internal strain due to uneventhen For instance, molten alloys are first rendered as homogeneous as possible by melting in high-frequency furnaces, and afterwards worked mechanically in such a way, that, in the first place, as great as possible elongation of the single crystals is attained. This is effected most advantageously, with material cast in the form of bars, by annealing and subsequent working down in a train of rolls, as finely graded as'possible, to a small sheetmetal-, tapeor wire-thickness. During this working, the material is subjected to one or several intermediate annealings, which should be as few as possible, in order to again recrystallize, the crystallite, which in the meantime had been considerably elongated by working. Towards the end of this operation, which is subject to variations with regard to the elongation, the details of the train of rolls or the annealing such as would occur to anyone skilled in the art, the material is worke in a cold state and brought into its final state of sheet metal, tape, or wire by a series of elongations by working without intermediate annealing. The material is allowed to remain in this final state, and is subjected to-no final thermic treatment whatever.

at'higher temperatures.

The following example of carrying out the process is given:

As initial material, 50-50 iron-nickel alloy is employed, in bar-form. This is first homogenized by annealing at 800 to 900 for about an hour, whereupon it is elongated, to such an extent that a cross-sectional reduction of 10% results. It is then annealed for an hour at 900, then again elongated while cold,

and so on. The elongation and intermediate anneallng are repeated in the same way three times. After the third annealing, the mapossess an initial permeability which is less than that of ordinary iron. However, they possess favorable values of hysteresis and of magnetic stability. If for instance, a 50-50 iron-nickel alloy is employed having an loss: be: equivalent;- to an effective increase initial; permeability of about 52', the hysteresis a number of other alloys of ferromagnetic substances" can be treated, also with the addition of silicon, manganese,'copper or similar substances, influencing the magnetic and mechanical properties. The magnetic values of the wires, tapes, sheet-metal or similar'materials, produced accordingto this process,

correspondsubstantially with those of the above-mentioned example.

The magnetic materials produced according to the invention, are particularly suited to; the; production of cores for Pupin-windings with sheet-metal-, tape or wire-cores,

as also as wires for over-spinning copper-.

conductors in Krarup-cable, because it is now possible to construct devices of this kind with closed magnetic circuits without air-gaps and in spite of this to attain high stability and permeability. Owing to the small hysteresis losses of the magnetic material, cables of this kind are particularly suitable for broadcasting transmissions. Also the substances made in accordance with the process of the invention can be pulverized and used in dust cores,

I the transmission of speech, it is of importance that they retain their properties under all which are notable for small variations of permeability with current and fortheir insensitiveness' to the magnetic influence of intense fields.

For the magnetic loading employed in long-distance transmission, particularly for working conditions. In connection with windings and Krarup-conductors, this is predominantly the inductivity. Although it is particularly well known, that, by the employment of magnetic materials of high permeability, a considerable saving of material can 'be attained by reducing the dimensions of cores, forsuch windings, the relatively low permeabilities of dust cores have been con'-' sidered suflicient. Cores of compressed pulverized, iron were employed, solely because such cores possess more stability, than all known materlals 1n sohd form, 1. e.:, in

the form of sheet-metal, tape or wire cores.

' temporary influence of more intense fields,

such as are produced, in working, posm'bly by the effect-of measuring, signalling or disturbing currents. In connection with Pupinwindings, it is prescribed, for instance, that the inductivity and thus the permeability shall not vary to the extent of 2%, when influenced by any fieldstrengths whatever up to about 50 ampere turns per cm. It has consequently become usual, to designate briefly as Stability, the highest alteration per cent, which can'be caused by field-intensities within this limit. Of course in accordance with this method of designation, the stability ,is greater; the less this number is, which more accurately stated, measures the Instability. By stable in this specification, we mean relatively little influenced by intense temporary fields.

'The changes in the permeability, owing to such influences, constitute a special property of magnetic materials. For solid materials the lowest values of variation in inductance, hitherto known, therefore the great est stabilities, always hitherto amounted to at least 30%. The exclusive employment-0f cores made of aggregations of' powdered materials in Pupin-windings, serves as proof of the fact, that with the state of the art as it is today, the attainment of the required stability with solid material is looked upon as impossible, although numerous materials are known, which possess other desirable magnetic properties, such as very high permeability, which should therefore enable the production of especially small windings.

What we-claim as new and desire to secure by Letters Patent of the United States, is:

1. The method of treating magnetic material to increase its magnetic stability which comprises successively annealing and forcibly elongating the material and, finally, after the final annealing,further forcibly elongating the material for application as a magnetic body.

2. The method of treating magnetic nickeliron alloy magnetic materials, including those having other substances, such as manganese, silicon and copper added, to increase the stability of their magnetic properties which comprises alternately annealing and working the material and finally cold working it to elongate it .as the final step of the treatment.

lnwitness whereof, we have hereunto set our hands this 26th day of June 1930.

ROBERT GOLDSCHMIDT.

HELMUT SPRUNG. 

